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Status Not under consideration
Workspace Db2 for z/OS
Created by Guest
Created on Mar 15, 2018

RELATED IDEAS

Index on expression should be used when outer join is rewritten (by the optimizer) as an inner join

When coding the following query (or, generalized query), an index on expression for UPPER(RTRIM(TABB.COLA)) is not used:

SELECT ...
FROM
....
TABA LEFT JOIN TABB ON ....
WHERE UPPER(RTRIM(TABB.COLA)) = ?

In the above query, it is (originally) written as a "left outer join", but because of the predicate, it can be rewritten as an inner join. And, if this was a simple predicate on TABB.COLA, DB2 would rewrite this as an inner join and a index with a leading column of TABB.COLA could be used (and generally would be used).

However, when the query is coded with an expression (as shown above), and a matching index (on expression) is available to be used, that index is not chosen to optimize this query.

I would like for DB2 to use the same query rewrite logic here as if the predicate was a simple predicate and then if an "index on expression" was available to use, it would be used.
  • Admin
    Janet Figone
    Reply
    |     Dec 30, 2020

    Thank you for submitting this Db2 for z/OS enhancement request. We have reviewed this request and believe it may a good candidate for the Db2 for z/OS product. However, it is not in our current roadmap and we are unable to deliver it within the next 24 months. Therefore, unfortunately, we will not be implementing this Idea.

    We appreciate your input to the Db2 for z/OS development team. We also hope that you will continue to submit ideas for improvements as customer feedback is a key component to shaping the future direction of Db2 for z/OS.

    Sincerely,

    Db2 for z/OS Team

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